* {
    margin: 0;
    padding: 0;
}
body {
    height: 100vh;
    background: #24292e ;
    font-size: 16px;
    color: #fff;
}

h1 {
    position: absolute;;
    left: 50%;
    transform: translate(-50%, 200%);
    font-size: 3em;
    color: #fff;
    letter-spacing: .05em;
}

input,
button {
    outline: none;
    background-color: transparent;
    border: none;
    outline: none;
}

input {
    -webkit-text-fill-color: #fff; 
}

input:-webkit-autofill {
    transition: background-color 5000s ease-in-out 0s;
  }

.loginBox {
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
    width: 400px;
    height: 364px;
    padding: 40px;
    background-color: rgba(0, 0, 0, 0.5);
    box-shadow: 0px 15px 25px 0 rgba(0, 0, 0, 0.6);
    box-sizing: border-box;
}

h2 {
    text-align: center;
    color: #fff;
    margin-bottom: 30px;
}

.item {
    position: relative;
    height: 45px;
    margin-bottom: 1px solid #ffffff;
    margin-bottom: 40px;
    border-bottom: 1px solid #fff;
}

.item input {
    width: 100%;
    height: 100%;
    padding-top: 20px;
    color: #fff;
    box-sizing: border-box;
}

.item input:focus+label,
.item input:valid+label{
    top:0;
    font-size: 12px;
    transition: all 0.2s linear;
}

.item label {
    position: absolute;
    left: 0;
    top: 12px;

}

.btn {
    position: relative;
    margin-top: 30px;
    margin-left: 240px;
    padding: 10px 20px;
    border: 1px solid transparent;
    color: #fff;
    overflow: hidden;
    border-radius: 5px;
    color: #fff;
    box-shadow: 0 0 5px 0 #03e9f4;
    letter-spacing: 2px;
}

.btn>span {
    position: absolute;
}

.btn>span:nth-child(1) {
    width: 100%;
    height: 2px;
    background: -webkit-linear-gradient(left, transparent, #03e9f4);
    left: -100%;
    top: 0;
    animation: line1 1s linear infinite;
}

@keyframes line1 {
    50%, 100% {
        left: 100%;
    }
}

.btn>span:nth-child(2) {
    width: 2px;
    height: 100%;
    background: -webkit-linear-gradient(top, transparent, #03e9f4);
    right: 0;
    top: -100%;
    animation: line2 0.5s linear infinite;
}

@keyframes line2 {
    50%, 100% {
        top: 100%;
    }
}

.btn>span:nth-child(3) {
    width: 100%;
    height: 2px;
    background: -webkit-linear-gradient(left, transparent, #03e9f4);
    left: 100%;
    bottom: 0;
    animation: line3 1s linear infinite;
}

@keyframes line3 {
    50%, 100% {
        left: -100%;
    }
}

.btn>span:nth-child(4) {
    width: 2px;
    height: 100%;
    background: -webkit-linear-gradient(top, transparent, #03e9f4);
    left: 0;
    top: 100%;
    animation: line4 0.5s linear infinite;
}

@keyframes line4 {
    50%, 100% {
        top: -100%;
    }
}